A pair of optical fibers can be coupled by projecting the end of each fiber through a contact and forming the fiber tip into a lens. The lenses transmit light between the optic fibers even though the spacing and alignment of the lenses is anywhere within a moderate range. Lensing, or the formation of an end portion of an optical fiber into a bead or lens, can be reliably accomplished by heating the fiber with an electric arc. The tips of a pair of electrodes are positioned on opposite sides of an end portion of an optic fiber which lies at a cross-aperture in the end of the contact. The fiber may have a diameter of about 0.005 inch while the contact has a diameter of about one-tenth inch, so the arc must pass through a tiny region. In prior attempts to establish the arc, it has been found that the arc sometimes passes around the side of the contact rather than across the optic fiber end portion.
Electric arcs have been used in the past to soften the ends of optic fibers to join them, although without heating the ends so much as to deform them into a lens or the like. The spliced fiber ends did not lie in a contact during splicing, and electrodes were placed closely on either side of the ends to be spliced, to assure that the arc would reliably heat the ends. However, it is found that when the same setup is used to form a lens at the end of an optic fiber, that the arc established between the electrodes quickly becomes erratic, in that the arc changes in its path and the sizes of the lenses become erratic (sometimes larger and sometimes smaller) and the shapes erratically deviate from spherical. A system for forming lenses at the ends of optic fibers by heating with an electric arc, which enabled close and reliable control of the arc while assuring at least a moderate electrode life, would be of considerable value.